The co-coking of hydrotreated decant oil (DO)/coal blends using a large laboratory-scale delayed coker was studied. DO was hydrotreated at several levels of severity for use in the co-coking work. Increasing the hydrotreatment severity increased the levels of hydrodesulfurization (from 50.6 to 99.0%) and hydrodenitrogenation (from 7.7 to 88.7%). Hydrotreatment resulted in increased amounts of paraffins, saturated cyclics, alkylbenzenes, two-ring aromatics, and hydroaromatics but decreased the amount of three-ring and larger compounds in the liquid. The coke yield from delayed co-coking of hydrotreated DOs and coal blends was observed to be in the range of 15.9-24.4%. Distillate liquid obtained from delayed co-coking increased with hydrotreating severity of DOs (from 71.0 to 76.2%). The boiling point distribution of the distillate liquid products was determined using fractional vacuum distillation. The results from vacuum distillation reveal that the percentage of the liquid products corresponding to jet fuel and diesel boiling ranges increases with an increasing hydrotreatment level. Characterization of gasoline, jet fuel, and diesel fractions was conducted using gas chromatography/mass spectroscopy (GC/MS). The GC/MS results of the gasoline fractions indicate a dominance of paraffins, saturated cyclics, and benzenes. Characterization of the jet fuel fractions shows that two-ring aromatics and hydroaromatics are present in the fuel in addition to paraffins, saturated cyclics, and benzenes. No polycyclic aromatic compounds were observed in jet fuel fractions. The diesel fuel fraction was mostly comprised of alkyl-substituted benzenes, naphthalenes, and three-ring and larger (more condensed) compounds.